Ovens or furnaces which are operable in excess of 2500.degree. F. are typically lined with dense refractory materials, such as firebrick. Such materials, because of their high density, usually have relatively high heat storage capacity resulting in significantly long periods of time being required to increase or decrease the temperature within the oven or furnace. Thus, such dense refractory materials hinder the cyclical operation of an oven or furnace by greatly increasing cycle time. In view of the foregoing, the lower density and resulting reduced heat storage capacity of ceramic fiber material makes such material desirable as a lining for those ovens and furnaces which operate in a cyclical manner and which approach and/or exceed an operating temperature of 2500.degree. F.
Ceramic fiber materials have been utilized as linings for ovens or furnaces for some time. It has been found that standard alumina-silica ceramic fiber blankets, when used as a lining material, exhibit excessive shrinkage at extremely high temperatures. Similarly, it has been found that high alumina-ceramic fibers cannot be formed into blankets with sufficient strength to be used as a lining material. The most common approach for overcoming these limitations is to vacuum form a "blend" of standard alumina-silica ceramic fibers and high alumina ceramic fibers into boards or modules which can be cemented to the surface of conventional refractory material. This approach puts the low density, thermally efficient ceramic fiber material on the "hot" side of the lining where it can have a significant effect, but does not provide the full advantage of a completely ceramic fiber lining since refractory material is still utilized as the "back-up" material.
Another approach that has been utilized is to use boards of "blended" ceramic fibers as the final layer in a multi-layer type lining. With this approach several layers of alumina-silica ceramic fiber blankets are impaled over high alumina "spike" anchors. The final layer in such an installation is a "blended" ceramic fiber board held in place by high alumina washers which fit into notches in the spikes. Although this approach has produced satisfactory results in ovens or furnaces operating at less than 2500.degree. F., it has been found that growth, warpage and breakage of the boards occur in installations operating in excess of 2500.degree. F.
A still another approach that has been investigated is to cement modules formed from high temperature ceramic fibers to "back-up" linings formed from lower temperature ceramic fibers. It has been found with this approach that the resulting composite material will adhere to the vertical walls of the oven or furnace but not to the top surface thereof. Further investigation has revealed that the strengths of the refractory cements or mortars that are utilized to hold the two ceramic fiber layers together have definite limitations, and typically there is some devitrification of the lower temperature ceramic fiber near the cemented interface between the ceramic fiber layers. Such devitrification reduces the fiber strength in the general area of the interface. Typically, the cement provides sufficient bonding and holding strength to hold the composite material to the vertical walls of the oven or furnace, but gravity overcomes the bonding and holding strength of the cement on overhead surfaces thus causing the modules to pull away from the lower temperature ceramic fibers utilized as the "back-up" lining.
Because of the foregoing, it has become desirable to develop a means for attaching together two layers of ceramic fiber material so that the resulting assembly can be utilized in any orientation in an oven or furnace which operates at very high temperatures.